1. Field of the Invention
The present invention relates generally to a slider for slide fasteners, and more particularly to a slider to be used on slide fasteners which require an extremely great force so as to open and close the same, such as a large-sized slide fastener or a heavy-duty slide fastener for industrial use.
2. Description of the Prior Art
A slide fastener of the type described has suffered from drawbacks that there intrinsically arises considerable frictional resistance between the slider and interlocking fasteners elements reciprocating therethrough. The frictional resistance not only renders the reciprocation of the slider quite sluggish but also causes frictional abrasion on a guide channel of the slider, thus leading the slider to mulfunction even for a short period. For solving such a difficulty, West German Patent No. 1040474 proposes an attempt of providing a pair of guide rollers one in each of the opposed guide flanges.
This attempt has overcome the difficulty to some extent but it still remains unsatisfactory. In the conventional slider, the guide rollers are mostly embedded in the guide flanges with their respective parts exposed for rolling engagement with the respective fastener element rows running through the guide channel of the slider. Since the guide flanges themselves are very thin, the guide rollers embedded therein are very small in diameter as well. Since being minute in diameter, the guide rollers are very liable to stick in spaces between adjacent fastener elements of the mating element fastener element rows, so that the slider is prevented from smooth reciprocation along the fastener element rows.
Mere replacement of the small-diametered guide rollers with rollers of larger diameter would not result in solution of the difficulty. Since the guide rollers are mounted beside a junction portion of the Y-shaped guide channel where stringer tapes of the slide fastener are inclined to pucker or wrinkle during the reciprocation of the slider along the fastener element rows; if the guide rollers were large in diameter, the puckers of the stringer tapes are the more susceptible to be caught by and between the guide rollers and the guide flanges, thus obstructing the reciprocation of the slider.